* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
a {
  text-decoration: none;
  color: #000;
}
li {
  list-style: none;
}
body {
  background: #f2f2f2;
}
.menu {
  position: fixed;
  width: 220px;
  height: 100vh;
  top: 0;
  left: 0;
  background: #23262e;
  .logo {
    h1 {
      font-size: 18px;
      text-align: center;
      height: 50px;
      line-height: 50px;
      border-bottom: 1px solid rgba(0, 0, 0, 0.2);
      a {
        color: #fff;
      }
    }
  }
  ul {
    margin-top: 20px;
    .menu_item {
      position: relative;
      text-indent: 2em;
      cursor: pointer;
      color: #fff;
      min-height: 50px;
      // border: 1px solid red;
      line-height: 50px;
      span {
        margin-right: 5px;
      }
      .ico {
        position: absolute;
        top: 0;
        right: 15px;
        font-size: 12px;
      }
      .menu_down {
        display: none;
        .menu_down_item {
          background: #282b33;
          a {
            margin-left: -15px;
            display: inline-block;
            width: 80%;
            height: 100%;
            color: rgba(255, 255, 255, 0.7);
          }
        }
      }
    }
  }
}
main {
  width: 100%;
  padding-left: 220px;
}
header {
  height: 50px;
  background: #fff;
  box-shadow: 0px 0px 3px rgba(0, 0, 0, 0.2);
  .header_menu {
    float: left;
    margin-left: 20px;
    font-size: 2em;
    color: #444;
    line-height: 50px;
  }
  .user {
    position: relative;
    float: right;
    margin-right: 50px;
    line-height: 50px;
    color: #444;
    span {
      font-size: 14px;
      color: #444;
    }
    .user_down {
      top: 50px;
      left: -20px;
      width: 80px;
      text-align: center;
      background: #fff;
      position: absolute;
      opacity: 0;
      .user_down_item {
        transition: background;
        font-size: 14px;
      }
      @keyframes user_down {
        0% {
          opacity: 0;
          transform: translate(0, 20px);
        }
        100% {
          opacity: 1;
          transform: translate(0, 0px);
        }
      }
      .user_down_item:hover {
        background: rgba(0, 0, 0, 0.2);
      }
    }
  }
  .user:hover > .user_down {
    animation: user_down 0.3s;
    animation-fill-mode: forwards;
    opacity: 1;
  }
}
